Seasonal Dynamics Of Benthic Macrofauna In The Keta Lagoon


to influence habitat heterogeneity, possibly serving as strong predictors

macrofaunal assemblage and abundance in the Keta lagoon. Some I agoons a re dumping a reas for d isposal o f waste f rom u rban and i ndustrial

areas. In some places their water is used for the cooling o f generators o f electric

power plants, which return effluent of warmed water to the lagoon. Coastal lagoons

are economically important in their use for aquaculture facilities ((Day and Yanez-

Arancibia, 1985; De Wit, 2003). Coastal lagoons facilitate processes, particularly

those resulting in loss or accretion of natural wetland. Despite all these uses, most

coastal lagoons are unstable succumbing to the vagaries of climatic conditions.

Depending on the local climatic conditions, coastal lagoons exhibit salinity levells,

which ranges from completely fresh to hypersaline (i.e. salinity values above 35ppt)

(Knoppers et at., 1991), such high levels are tolerable to few organisms. However,

some coastal lagoons in Ghana are functionally stable because of the influence from

the sea that has one or more narrow opening(s) to the lagoons most of the time.

In Ghana, there are over 90 lagoons and wetlands along the entire 550 km coastline,

which among others, are important feeding/foraging sites for migratory birds (Armah,

1993). The largest among these, is the Keta lagoon. Together with its associated

wetlands, Keta lagoon has been estimated to be a bout 7 02 km2 in area (Armah,

1993). The water body however has an estimated surface area of 350 km2 (Ababio,

2001). This makes it the largest lagoonal wetland in West Africa. The lagoon is a

closed system and stretches for about 40km along the coast, separated from the sea

by a narrow coastal ridge or strip of land, which is only about 2.5 km at its widest

point and about 0.92 km at the narrowest portion (Piersma and Ntiamoah-Baidu,


In recent times the narrow strip of land separating the lagoon from the sea has

experienced very severe erosion from the sea leading to the inundation of the

peripheral settlements of the lagoon in the catchment area during periods of heavy

rainfall. The situation necessitated m itigating measures to be taken by the Ghana

Government to protect life and property with the initiation of the Keta Sea Defence

Work Project (KSDWP). The KSDWP is of five years duration. The construction activities were i nitiated in early 2000, a nd consisted of f our principal components,

namely, sea defence, land reclamation, construction of road and construction of flood

relief structure.

Under the Project a total area of approximately 283 ha of land would be reclaimed

by construction of groynes from the shore to a depth approximately 4.5 meters NLD

(National Land Datum) and extending 140 - 200 meters from the existing shore at

the seaward section. The project has also led to the dredging of portions of the

lagoon about 8 km long from Havedzi to Keta for road construction and land

reclamation. The principal biological impacts of such dredging activities include

disturbance and removal of benthos and alteration of the substrate upon which

colonization depends. Dredging activities also affect certain physical and chemical

conditions such as degree of oxygenation and mineralization, temperature, salinity,

water flow, depth and fluctuations of water level. Some of these changes, beside

protecting life and property will also enhance the ecological conditions of the lagoon

in terms of fisheries. For instance, the author observed lots of Mugil sp. and crabs

(e.g. Uca tangeri) in the dredged channel created by the project. In spite of these

and others of ecological importance that have earned the Keta lagoon the position of

a Ramsar Site and the high fisheries yield, very little benthic work has been carried

out. Benthic-pelagic coupling is known to drive fisheries of coastal lagoons (Kjerfve,


Benthic invertebrates are essential to the ecology of coastal water bodies. Many

benthic species are themselves harvested for human consumption, and they also

provide the means by which primary food resources are passed up the food chain to

fish. Changes in the structure of benthic communities are now used routinely in

several countries to monitor the biological effects of man's activities in coastal

waters, pollution, and disturbances caused by major engineering work (dredging) etc.

Most researches on benthic communities have been conducted in temperate

latitudes, and to a lesser extent, subtropical and boreal (mountaneous) latitudes

(Gray, 1981). However, with currently increasing interest in bio-diversity coupled with

industrialization and urbanization near water bodies, it seems timely to undertake

comparable studies in a tropical area such as Ghana.

Most early work was necessarily taxonomic or consisted o f compilations of faunal

lists. Hence, little comprehensive work exists detailing factors affecting the

distribution and abundance of soft-bottom benthic assemblages in the tropics

(Longhurst and Pauly, 1987). Information on seasonal variability of macrobenthic

fauna in lagoonal systems is very scanty. The Keta lagoon is no exception in

particular, its macrobenthic fauna.

The only benthic investigation in the Keta lagoon was carried out by Finlayson et al.,

(2000). It however, lacks certain critical elements. These are (1) explanation for the

distribution pattern of macrofauna (2) assessment of the organic matter and sulphur

contents in the sediment; (3) intervals between sampling stations were approximately

2 km but such a long interval has a potential danger of masking valuable information

on habitat structure, and lastly but quite significantly (4) the study was restricted to a

short period between November and December and hence could not explain

seasonality or otherwise of the distribution and abundance of benthic macrofauna as

well as habitat structure. Thus, the macrofaunal information of the Keta lagoon from

the work of Finlayson et al., (2000) may be severely distorted by lack of adequate

data on temporal and spatial variability. The abundance and spatial distribution of

macrofauna assemblages determine, to a large extent, the composition of higher

trophic organisms of commercial importance such as fishes and birds (Kjerfve, 1994;

Colwell and Landrum, 1993; Liang et al., 2002). Understanding the observed patterns

of distribution and abundance of organisms often must involve an evaluation of the

relationship between these organisms and the structure of the habitat.

This study was therefore, undertaken to investigate the seasonal dynamics of benthic

macrofauna distribution and abundance in relation to environmental variables of the

Keta lagoon. The studyl provides an understanding into benthic ecology in the Keta

lagoon. The study also will provide animportant baseline information on the likely

long-term impacts of constructional activities of Keta Sea Defence Work Project and

anthropogenic impacts of the settlements around the lagoon especially from the

growing populations on the coastal belt.

The specific objectives of the study are to:

(i) analyse, in detail, the benthic macrofauna distribution pattern and

abundance in the Keta lagoon at spatial and temporal scales that will

better explain the relationships between the organisms and habitat


(ii) investigate the key environmental (physico-chemical parameters)

variables affecting the benthic macrofaunal community structure

(iii) Further, the study will assess

(a) the recolonisation/colonization of benthic macrofauna in the modified sections of

the lagoon as a result of the KSDWP, notably, dredged canal and areas impacted

by dredge spoil, and

(b) sediment distribution and its relationship to spatial occurrence of the macrofauna

as well as provision of sediment map of the lagoon.

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LAMPTEY, E (2021). Seasonal Dynamics Of Benthic Macrofauna In The Keta Lagoon. Afribary. Retrieved from

MLA 8th

LAMPTEY, EMMANUEL "Seasonal Dynamics Of Benthic Macrofauna In The Keta Lagoon" Afribary. Afribary, 17 Apr. 2021, Accessed 14 Jun. 2024.


LAMPTEY, EMMANUEL . "Seasonal Dynamics Of Benthic Macrofauna In The Keta Lagoon". Afribary, Afribary, 17 Apr. 2021. Web. 14 Jun. 2024. < >.


LAMPTEY, EMMANUEL . "Seasonal Dynamics Of Benthic Macrofauna In The Keta Lagoon" Afribary (2021). Accessed June 14, 2024.